The invention relates to optical readers in general and in particular to a method for operating an optical reader having a 2D image sensor.
Optical readers having 2D image sensors commonly are used to read both 1D and 2D symbols. Some optical readers having a 2D image sensor read a 1D symbol by capturing a 2D image representation, or xe2x80x9cframexe2x80x9d of image data corresponding to a target area which comprises a 1D symbol, and launching a scan line or lines in order to attempt to decode for 1D symbols which may be represented in the area. Other optical readers having 2D image sensors read 1D symbols by capturing a 2D image representation of an area containing the 1D symbol, preliminarily analyzing the image data represented in the area to determine that the image data comprises a representation of a 1D symbol, and then launching a scan line in an attempt to decode for the 1D symbol determined to be present. In either case, a full frame 2D image representation is captured in order to decode for a 1D symbol.
Capturing a 2D image representation requires a substantial amount of time, especially in applications wherein one or more xe2x80x9ctestxe2x80x9d frames of image data must be captured prior to capture of a frame that is subjected to processing as are explained in commonly assigned application Ser. No. 09/766,922 entitled xe2x80x9cOptical Reader Having Reduced Parameter Determination Delayxe2x80x9d filed concurrently herewith and incorporated herein by reference. Furthermore, assuming a constant processing speed, the dine required for an optical reader to capture a 2D image representation increases with the resolution of the image sensor which is incorporated in the reader. Currently available CMOS mega pixel image sensors have low frame clock out rates of about 15 frames per second (FFS).
A user""s satisfaction with an optical reader often varies directly with the decoding speed of the optical reader. Given that higher resolution, including mega pixel readers, are expected to grow in popularity, the frame capture time will become an increasingly important factor for consideration in performance of an optical reader.
The invention is a method for configuring an optical reader having a 2D image sensor so the reader captures and processes image data at higher speeds.
According to the invention, a control circuit of an optical reader equipped with a 2D image sensor is configured to operate in a partial frame operating mode. In a partial frame operating mode, the control circuit clocks out and captures less than a full frame of image data and processes that image data. The control circuit may process the image data of the partial frame, for example, by reading the image data from memory and outputting the image data to an output location such as a display device or a processor system in communication with the reader, by reading and attempting to decode decodable symbols which may be recorded in the partial frame, or by reading and performing optical character recognition on characters represented in the partial frame of image data.
In one embodiment, the partial frame operating mode is employed to clock out and capture image data corresponding to at least one linear pattern sufficient so that a 1D symbol in the field of view of the image sensor may be decoded without clocking out and capturing an entire frame of image data. The partial frame of image data that is clocked out from the image sensor during the partial frame capture operating mode may be, for example, a row of symbols at or near the center of the image sensor or a limited number of lines of image data corresponding to pixel locations of the image sensor, possibly at varying angular orientations. The control circuit may be configured so that if the control circuit cannot decode a 1D symbol during the course of operating in the partial frame capture mode, or detects that a 2D symbol is represented in the captured image data, the control circuit switches operation to a full frame capture mode.
In another embodiment, the partial frame operating mode is employed to clock out and capture pixel values corresponding to a grouping of pixels at or near a center of an image sensor other than a linear pattern of pixels. This embodiment may be advantageously employed in cases where decodable symbols are expected to be concentrated proximate a center of an image sensor""s field of view. A control circuit may be configured so that if the control circuit cannot decode a symbol represented in the partial frame, or determines that a symbol is represented partially or entirely outside the image data of the partial frame, the control circuit automatically switches operation to a full frame image capture mode.
These and other details, advantages and benefits of the present invention will become apparent from the detailed description of the preferred embodiment hereinbelow.